The present invention relates to a device for calibrating cooling of an extruded synthetic profile having a water tank through which cool water can flow through cool water supply and outlet pipes, which extends longitudinally in the direction of extruding and is subdivided into individual cooling chambers by means of calibrating diaphragms spaced at a mutual distance in series in the direction of extruding.
With extrusion of synthetic profiles, window profiles made of PVC for example, after the extruder and the molding profile nozzle for exact-size cooling most times the profile billet is first guided through a dry calibrator and then through a wet calibrator, whereby the wet calibrations operate with either a spray bath or a full bath. Spray baths, in which cool water is sprayed onto the profile billet to be cooled by way of a plurality of spray nozzles, contribute a major cooling effect, but they are expensive on account of the danger that the nozzles might stop up as they are interference-prone and are also associated with high water consumption. In full baths the synthetic billet to be cooled is on the other hand guided through a water tank filled with coolant and thereby drawn through calibration apertures, resulting in less structural expense and lower water consumption, although the cooling effect remains unsatisfactory.
To improve the cooling effect it has been proposed according to EP 0 659 536 to provide the calibration apertures of the water tank, in addition to the apertures, with other openings for generating a turbulent flow of the cool water in the cooling chambers. This coolant flow requires a differential pressure between inlet and outlet sides of the calibration apertures, whereby only a very limited differential pressure is available in the water tank and it is a question of moderate eddying of the coolant as it flows through the turbulence openings. The additional cooling effect attainable via the turbulent flow is accordingly insufficient. Furthermore, all the coolant must flow through the individual chambers, making it impossible for the quantity of coolant in the cooling chambers to match the actual cooling requirement and whereby the consumption of coolant cannot be minimized. If, for the purpose of increasing the geometrical security of the profile, the water tank is impacted with negative pressure on account of the large quantities of flowing water in conjunction with the suctioned excess air there is the risk of undesired fluctuations which lead to variations in pressure and thus to negative effects on the profile geometry.
Similar ratios result from a cooling device according to DE 195 04 981 A which has a negative-pressure water tank subdivided into chambers by calibration apertures, whereby additional longitudinal walls on the underside of the profile billet together with through-flow openings arranged alternatively and laterally compel the coolant to flow not only along the profile billet, but around it also.
EP 0 811 472 A discloses a calibrating device having a water tank subdivided by calibrating apertures, whose coolant flow is set so low that a laminar flow limit layer results on the profile billet, which layer should be stripped as it passes through the calibrating apertures and thus the desired heat removal is to be attained. It must be doubted as to whether the cooling effect is to be improved by preventing forced turbulence. Also, zones can arise in which the coolant lingers for an exceptionally long time and takes on higher temperatures, by which the cooling effect suffers in any case.
The objective of the present invention is to produce a device of the type initially indicated, which guarantees an effective and highly efficient cooling of billets with relatively minimal structural expense.
The invention solves this task in that a coolant supply pipe terminates in each cooling chamber and the cooling chambers are connected to a coolant outlet by means of an outlet aperture. The cooling chambers are impacted with coolant by this coolant arrangement, such that the cooling effect can be best adapted to the actual cooling requirement. The coolant influx quantity can be matched precisely to the minimum required quantity of coolant, resulting in exceedingly economical water consumption. In addition, when the coolant flows out of the outlet openings of the coolant supply pipe it entrains corresponding turbulence flows in the chambers, leading to heat equalization of the water in the cooling chambers and considerably increasing the billet cooling as a result of turbulently flowing surface layers. On account of the coolant flowing into each chamber and the resulting coolant efflux the influx of already warmed coolant from other chambers is stopped and thus securely prevents impairment of the cooling effect in the chambers. Not last the individual coolant impact of the chambers is extensively independent of pressure level in the water tank and accordingly is best suited to the combination with a subpressure tank for raising the dimensional stability as the profile billet is being cooled.
If the coolant supply comprises a supply pipe laid along the water tank and having at least one outlet bore or nozzle, an adequate water supply to the individual cooling chambers can be provided economically, whereby the influent quantity of water and the flow intensity and turbulence of the water flow per chamber are adjusted by variation of the number and/or diameter of these outlet bores and can thus influence the cool flow inside the chambers.
Pipes particular to removal of the coolant could be provided, yet it is an advantage if an outlet channel extending in a longitudinal tank direction above and/or below the calibration apertures is provided as coolant outlet and the cooling chambers opening upwards or downwards form the outlet openings with their open sides assigned to the outlet channel(s). Because of this in the water tank there needs to be adequate free space only for the effluent coolant to be left free between the calibrating apertures and the tank cover and/or between the calibrating apertures and the tank floor and the coolant can flow out almost without pressure. Depending on the structure of the water tank or application of the calibration apertures the outlet channel can be effectively installed in the cover or floor area and it is understandably also possible to provide outlet channels both in the cover and the floor area to further benefit the coolant efflux and to thus minimize the flow rate.
If the outlet openings are covered over by an apertured plate or similar any unwelcome influx of the already warmed coolant from adjoining chambers is securely prevented on account of the flow resistances increased with the apertured plates.
In accordance with another embodiment of the present invention a discharge chamber free of supply pipes is arranged after the cooling chambers in the flow direction of the coolant discharge, into which the coolant outlet discharges by way of an overflow formed by the calibrating aperture between discharge chamber and adjoining cooling chamber and from which two suction pipes, a lower water suction pipe and an upper air suction pipe proceed. Since the entire quantity of coolant must flow out by way of the overflow, the water level in the cooling chambers has to be preset by the altitude of this overflow. Further, the prerequisite for simple separate suctioning of water and air is offered by the discharge chamber, whereby the lower suction pipe conveys water almost continuously and the upper suction pipe essentially suctions air and spray water, if required, so that there are no fluctuations in pressure in the water tank due to a common water/air discharge. It is accordingly possible to avoid a particular separating tank for separating air and water without the vacuum pump being damaged by an excessive proportion of water in the suctioned air.